<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>一起拿红包</title>
</head>
<style>
    *{
        padding:0;
        margin:0;
    }
    div{
        background: url('/img/coupon2.png') no-repeat center;
        background-size: contain;
    }
</style>
<body>
<div id="backPic">

</div>
<script>
    var backPic=document.getElementById('backPic');
    var w=document.body.clientWidth;
    backPic.style.height=1206*w/750+'px';
    backPic.style.width=w+'px';
</script>
</body>
</html>